Structural basis for mouse LAG3 interactions with the MHC class II molecule I-Ab

The immune checkpoint protein, Lymphocyte activation gene-3 (LAG3), binds Major Histocompatibility Complex Class II (MHC-II) and suppresses T cell activation. Despite the recent FDA approval of a LAG3 inhibitor for the treatment of melanoma, how LAG3 engages MHC-II on the cell surface remains poorly understood. Here, we determine the 3.84 Å-resolution structure of mouse LAG3 bound to the MHC-II molecule I-A